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Abstract:

An apparatus for placement on or in a body of water for hyperspectral
imaging of material in the water comprises an artificial light source and
a hyperspectral imager. These are arranged so that in use light exits the
apparatus beneath the surface of the water and is reflected by said
material before re-entering the apparatus beneath the surface of the
water and entering the hyperspectral imager. The hyperspectral imager is
adapted to produce hyperspectral image data having at least two spatial
dimensions.

Claims:

1. An apparatus for placement on or in a body of water for hyperspectral
imaging of material in the water comprising an artificial light source
and a hyperspectral imager which are arranged so that in use light exits
the apparatus beneath the surface of the water and is reflected by said
material before re-entering the apparatus beneath the surface of the
water and entering said hyperspectral imager, wherein said hyperspectral
imager is adapted to produce hyperspectral image data having at least two
spatial dimensions, and wherein the apparatus is arranged to estimate a
spectral attenuation coefficient of the ambient water and to adjust the
spectral output of the artificial light source so that a predetermined
light spectrum arrives at said material.

2. (canceled)

3. An apparatus as claimed in claim 1 comprising one or more optical
filters selectably placeable in the path of the emitted light so as to
adjust the spectral output of the artificial light source.

4. An apparatus as claimed in claim 3 comprising a plurality of optical
filters selectably placeable in the path of the emitted light, each
having a unique spectral-filtering characteristic.

5. An apparatus as claimed in claim 1 wherein the light source comprises
a plurality of light-emitting elements each with differing emission
spectra, and wherein the apparatus is configured to alter the power
supplied to respective light-emitting elements in order to give a
required overall output spectrum.

7. An apparatus as claimed in claim 1 comprising an optical sensor and
logic for estimating a spectral attenuation coefficient of the ambient
water using an output from said optical sensor.

8. An apparatus as claimed in claim 1 wherein the hyperspectral imager
operates using dispersive spectrography.

9. An apparatus as claimed in claim 1 wherein the hyperspectral imager
has no independently moving parts.

10. An apparatus as claimed in claim 1 arranged so that movement of the
apparatus through the body of water enables an area of interest to be
continuously imaged.

11. An apparatus as claimed in claim 1 comprising a tether for connecting
to a ship or other vessel.

12. An apparatus as claimed in claim 11 wherein the tether comprises an
umbilical power supply.

13. An apparatus as claimed in claim 1 comprising a portable power supply
and wherein the apparatus is capable of independent movement.

14. An apparatus as claimed in claim 13 wherein the portable power supply
comprises a battery.

15. An apparatus as claimed in claim 1 further comprising an image
capturer for capturing frames from the hyperspectral imager.

16. An apparatus as claimed in claim 15 further comprising image
processing logic arranged to process captured images from the
hyperspectral imager.

17. An apparatus as claimed in claim 1 adapted to be fully submersible.

18. An apparatus as claimed in claim 17 comprising a housing designed to
withstand external pressures of at least 10 bars.

19. An apparatus as claimed in claim 1 wherein the hyperspectral imager
is arranged to provide a spectral resolution of finer than 1 nm.

20. An apparatus as claimed in claim 1 wherein the hyperspectral imager
is arranged to image over the whole spectrum of visible light.

21. An apparatus as claimed in claim 1 wherein the hyperspectral imager
has a maximum physical dimension of less than 50 cm.

22. An apparatus as claimed in claim 1 wherein the hyperspectral imager
weighs less than 1 kg.

23. An apparatus as claimed in claim 1 wherein the hyperspectral imager
consumes less than 2 Watts.

24. A method of imaging material beneath the surface of a body of water
comprising: illuminating said material with an artificial light source
from beneath the surface of the water; receiving from beneath the surface
of the water light reflected from said material into a hyperspectral
imager; said hyperspectral imager generating hyperspectral image data
from said material, said image data having at least two spatial
dimensions; estimating a spectral attenuation coefficient of the ambient
water; and adjusting the spectral output of the artificial light source
so that a predetermined light spectrum arrives at said material.

25. A method as claimed in claim 24 wherein the artificial light source
is provided in the same unit as the imager.

26. A method as claimed in claim 24 comprising use of apparatus for
placement on or in a body of water for hyperspectral imaging of material
in the water, comprising an artificial light source and a hyperspectral
imager which are arranged so that in use light exits the apparatus
beneath the surface of the water and is reflected by said material before
re-entering the apparatus beneath the surface of the water and entering
said hyperspectral imager, wherein said hyperspectral imager is adapted
to produce hyperspectral image data having at least two spatial
dimensions, and wherein the apparatus is arranged to estimate a spectral
attenuation coefficient of the ambient water and to adjust the spectral
output of the artificial light source so that a predetermined light
spectrum arrives at said material.

27. (canceled)

28. A method as claimed in claim 24 comprising the further step of using
the hyperspectral imager to determine whether a predetermined spectrum
for the artificial light is achieved.

29. A method as claimed in claim 24 comprising the further step of using
an optical sensor to determine whether a predetermined spectrum for the
artificial light is achieved.

30. (canceled)

31. A method as claimed in claim 24 wherein said estimating is
continuous.

32. A method as claimed in claim 24 comprising the further step of
locating a spectral filter in the path of the artificial light.

33. A method as claimed in claim 24 comprising the further step of
selectively illuminating elements from among a set of spectrally-distinct
light-emitting elements.

36. A method as claimed in claim 24 further comprising: deploying a
calibration surface having known reflectance characteristics; and using
feedback control to alter the spectrum of light emitted by the light
source depending on the spectrum of the light reflected from the
calibration surface until a predetermined spectrum is achieved.

37. A method as claimed in claim 36 wherein the calibration surface is a
white Teflon disc and wherein the disc is deployed in front of the
hyperspectral imager at a given distance.

38. A method as claimed in claim 24 comprising the further step of
locating or mapping the extent of one or more organisms or other material
by the characteristic spectral fingerprint(s) thereof.

39. (canceled)

40. (canceled)

41. (canceled)

42. (canceled)

43. (canceled)

44. (canceled)

45. (canceled)

46. (canceled)

47. (canceled)

48. (canceled)

49. (canceled)

50. (canceled)

51. (canceled)

52. (canceled)

53. (canceled)

54. (canceled)

55. (canceled)

56. (canceled)

57. (canceled)

58. (canceled)

59. (canceled)

60. An apparatus for placement on or in a body of water for hyperspectral
imaging of material in the water comprising an artificial light source
and a hyperspectral imager which are arranged so that in use light exits
the apparatus beneath the surface of the water and is reflected by said
material before re-entering the apparatus beneath the surface of the
water and entering said hyperspectral imager, wherein said hyperspectral
imager is adapted to produce hyperspectral image data having at least two
spatial dimensions, and wherein the apparatus is arranged to estimate a
spectral attenuation coefficient of the ambient water and to compensate
for the attenuation of reflected or emitted light returning to the
apparatus.

61. A method of imaging material beneath the surface of a body of water
comprising: illuminating said material with an artificial light source
from beneath the surface of the water; receiving from beneath the surface
of the water light reflected from said material into a hyperspectral
imager; said hyperspectral imager generating hyperspectral image data
from said material, said image data having at least two spatial
dimensions; estimating a spectral attenuation coefficient of the ambient
water; and compensating for the attenuation of reflected or emitted light
returning to the apparatus.

Description:

[0001] This invention relates to hyperspectral imaging of aquatic
specimens and scenes.

[0002] When viewing a scene using a traditional digital imaging sensor or
by eye, the intensity of light from each point or pixel of the imaged
scene can be determined for each of three wavelength bands (centred
around red, green and blue for a digital camera, and yellowish-green,
green and bluish-violet for the human eye). Information about the full
spectral emissions (i.e. a continuous graph of intensity over wavelength)
of the scene can, at best, be represented in only a three-dimension
colour space, necessitating a loss of information.

[0003] Multispectral sensors have been used in research into aquatic
(freshwater, brackish water and salt water) environments for about 30
years. Multispectral sensors are divided into more than three discrete
colour bands and so give more detailed spectral information. They
typically have a minimum wavelength resolution of 10 nm. They have
typically been carried in satellites, aeroplanes, buoys and boats to
analyse upwelling radiance remotely, and in underwater vehicles to
measure both upwelling and downwelling radiance in situ. In both cases
the light measured by the sensor comes from natural illumination that is
incident on the water.

[0004] Hyperspectral sensors are also known. These have a much better
wavelength resolution than multispectral sensors--at least 10 nm or
better and can operate over a broad range of wavelengths including
visible light and typically also into ultraviolet and infrared
frequencies. It is also known to use hyperspectral sensors for imaging
purposes in passive remote sensing. A hyperspectral imager (also known as
an imaging spectrometer, imaging spectroscope, imaging spectroradiometer,
superspectral or ultraspectral imager), is capable of determining the
light intensity from each point or pixel of a scene for each of a large
number (typically hundreds) of wavelength bands, each no more than 10 nm
wide. This results in far more spectral information about the scene being
preserved than is the case when just three bands are available, as for
conventional imaging.

[0005] Because hyperspectral imagers give such detailed spectral
information for each pixel in the image, independently of each other, it
is possible to identify regions containing particular types of matter,
such as chemical substances and organisms, by using their known unique
spectra.

[0006] Applications for hyperspectral imagers include mineral exploration,
agriculture, astronomy and environmental monitoring. They are typically
used in aeroplanes (so-called "remote" viewing).

[0007] An overview of the use of hyperspectral sensors in oceanography is
given is "The New Age of Hyperspectral Oceanography" by Chang et al. in
Oceanography, June 2004, pp. 23-29. WO 2005/054799 discloses the use of a
hyperspectral imager from airborne platforms to observe coastal marine
environments remotely. The use of an airborne hyperspectral imager for
mapping kelp forest distribution close to the shore is described in "Kelp
forest mapping by use of airborne hyperspectral imager" by Volent et al.
in Journal of Applied Remote Sensing, Vol. 1, 011503 (2007).

[0008] However, the applicant has realised that taking hyperspectral
images remotely from the air or from space has several limitations. For
example, even for very optically clear water, such as can be found in the
Arctic, it is not possible to distinguish features of the sea bottom or
of suspended matter beyond a depth of a few metres. In more typical
marine waters, even this limited visibility is drastically reduced and is
normally less than a metre or so--in murkier waters maybe only a few
centimetres might be penetrable by light. This limits the usefulness of
this technique. Additional problems occur due to interference from the
air between the water surface and the remote imager; for example, due to
clouds and to Rayleigh scattering. It is also necessary to take into
account the angle of the sun in the sky. Furthermore, the spatial
resolution of conventional remote sensing systems, such as a
hyperspectral imager mounted in an aeroplane, is typically relatively
low.

[0009] When viewed from a first aspect the invention provides an apparatus
for placement on or in a body of water for hyperspectral imaging of
material in the water comprising an artificial light source and a
hyperspectral imager which are arranged so that in use light exits the
apparatus beneath the surface of the water and is reflected by said
material before re-entering the apparatus beneath the surface of the
water and entering said hyperspectral imager, wherein said hyperspectral
imager is adapted to produce hyperspectral image data having at least two
spatial dimensions.

[0010] In accordance with the invention there is provided a new method and
apparatus for aquatic hyperspectral imaging (optical measurements by
using artificial light sources) which open up the possibility for wider
and more accurate uses of hyperspectral imagers in underwater
environments. Two-dimensional hyperspectral images of underwater material
can be obtained from in situ apparatus; i.e. apparatus that is at least
partially submerged. By having control of the light source, more accurate
measurements of reflectance and transmission characteristics can be made,
since there is no need to calibrate for solar angle above the horizon,
and there are no atmospheric distortions to worry about. Moreover
hyperspectral imaging can be carried out at any depth, rather than just
at the surface as with remote sensing approaches.

[0011] Moreover by carrying its own artificial light source, the apparatus
can be used to image material at much greater depths; either because it
can be made bright enough to penetrate further, or because the apparatus
itself can be submerged to the required depth. A further advantage given
by the on-board light source is that the emission spectrum of the light
source can be chosen or tailored to the reflectance spectrum of the
material being looked for or expected and the optical properties of the
water.

[0012] These optical properties are affected by coloured dissolved organic
matter, suspended matter, phytoplankton etc. Thus if a particular
material is being searched for, the light source can be chosen to ensure
that it is illuminated by all the desired wavelengths corresponding to
peaks in its reflection spectrum. Equally the appropriate light source
can be chosen absorption and scattering properties of the water in which
the unit is operating can be

[0013] For example an apparatus in accordance with the invention, such as
an autonomous underwater vehicle (AUV), remotely operated vehicle (ROV),
could be provided with a plurality of light sources. Each light source
could be used in different conditions or when looking for different
materials; or indeed they could be blended together in varying
proportions to give further lighting options.

[0014] Indeed in a set of preferred embodiments the apparatus comprises
means for adjusting the spectrum of light emitted by the light source or
by a plurality of light source. This allows the possibility of "tuning"
the overall spectral output of the light source(s) as needed. This could
be an adjustment made for each mission or could be adjusted
dynamically--either manually or under programmed or feedback control. For
example a calibration surface having known reflectance characteristics
could be deployed and feedback control used to alter the output spectrum
depending on the spectrum of the light reflected from the calibration
surface until a desired spectrum is achieved. A non-limiting example of
such a calibration surface is a white Teflon disc deployed in front of
the hyperspectral imager at a given distance.

[0015] The hyperspectral imager could though be calibrated using other
instruments such as a (non-imaging) spectroradiometer, spectrophotometer
or a spectrofluorometer. The apparatus may comprise further instruments
such as a spectrophotometer, a spectrofluorometer, an acoustic Doppler
current profiler (ADCP), a chlorophyll fluorescence sensor (passive Ch1 a
fluorometer (no artificial excitation light source), blue excitation
light stimulated Ch1 a fluorometer or LED laser Ch1a fluorometer), a
coloured dissolved organic matter (cDOM) sensor, a backscattering meter,
a turbidity meter, a temperature sensor or a salinity meter.
Determinations from these other instruments may be used to adjust the
output of the hyperspectral imager and/or the light source.

[0016] In one example the spectrum adjusting means could comprise one or
more optical filters selectably placeable in the path of the emitted
light. Preferably more than one filter is available, each filter having a
unique spectral-filtering characteristic. Alternatively or additionally
the light source may comprise a plurality of light-emitting elements each
with differing emission spectra, the spectrum adjusting means comprising
means for altering the power supplied to respective elements in order to
give a required overall output spectrum. The light emitting elements
could comprise light emitting diodes (LEDs). The LEDs could emit light
substantially at a single-frequency--e.g. red, green or blue light--or
could contain phosphors that emit light across a range of
frequencies--e.g. white light. A mixture of coloured and white LEDs could
be employed.

[0017] It is important to note that the present invention is not concerned
with simple hyperspectrometers (e.g. spectroradiometers) providing a
spectral analysis of effectively a single light beam travelling along a
single path. A hyperspectral imager on the other hand can produce a
two-dimensional representation of a scene containing hyperspectral
information for each of many points across the scene.

[0018] The addition of spatial dimension information over simple
hyperspectral sensor output data, allows hyperspectral imagers to be used
in a wide variety of applications. In general it allows the
identification of underwater material of interest in situ in an aquatic
environment (bio-geo-chemistry). This can have many useful applications
such as enhanced environmental monitoring; developing theme-maps of
materials of interest that are geolocalized and have a time tag; creating
a time-series of hyperspectral images of a region including a given
material of interest; monitoring and surveillance of materials of
interests in a given region; identification of unusual activities (e.g.
mass occurrence of a given organism, planktonic or benthic; oil leakage;
leakage of other minerals/chemicals; metal disintegration).

[0019] The hyperspectral imager could, for example, use dispersive
spectrography (DS), Fourier transform spectrography (FTS) or Hadamard
transform spectrography (HTS). Dispersive spectrography generates a
spectrum by optically dispersing incoming radiation according to its
spectral components while FTS and HTS use the Michelson interferometer
principle to generate a spectrum by modulating incoming radiation in the
time domain through interference by use of moving mirrors or a Hadamard
array respectively; the modulated radiation in the time domain is then
Fourier transformed into spectral components. Preferably the imager uses
dispersive spectrography; this reduces the need for moving parts and
permits a compact, robust and low-cost construction with relatively low
power consumption, and good resistance to the low temperatures that may
be experienced underwater. Preferably the imager operates using the
push-broom technique. Preferably movement of the whole apparatus (e.g.
forward motion of an underwater vehicle) enables an area of interest to
be continuously imaged; this contrasts with FTS and HTS approaches in
which separate, discrete images would need to be formed and then
assembled to image a large area. Preferably it has no independently
moving parts; this contrast with FTS which requires a moving mirror and
HTS which requires a moving grating or mask.

[0020] The apparatus could be tethered to a ship or other vessel. Such a
tether could comprise an umbilical power supply. Alternatively and
preferably the apparatus could move independently; e.g. it might comprise
a portable power supply such as batteries or means for generating its own
power. Whether tethered or untethered, control of the apparatus could be
exercised from a support vessel, or even from land, or the apparatus
could be completely autonomous. In some preferred embodiments the
apparatus is not physically connected to any above-surface apparatus, and
comprises a battery power supply, which may be lead-acid or nickel-based,
but is preferably lithium-based so as to be relatively compact and
light-weight. Alternatively or additionally, the apparatus may comprise
any other suitable power supply such as a combustion engine, a nuclear
reactor, or a capacitor (e.g. a super capacitors).

[0021] The apparatus preferably comprises image capture means, such as a
digital video camera, for capturing frames from the hyperspectral imager
for subsequent analysis; it may additionally or alternatively comprise
image processing means arranged to process captured images from the
hyperspectral imager; it may, for example, be arranged to compile
time-sequential frames into a representation of a scene.

[0022] The apparatus could be a floating vessel. In a set of preferred
embodiments however it is adapted to be fully submersible. Embodiments of
the invention comprise a housing made substantially of metal, e.g.
aluminium or marine steel. In a preferred set of embodiments part of the
housing or hull is transparent to permit the exit and entrance of light
from/to the light source and imager. For example it could comprise one or
more transparent panels, e.g. made of soda glass, quartz, acrylic glass
or other suitable material. In some embodiments, the entire housing could
be constructed of transparent material.

[0023] Alternatively the light source and/or hyperspectral imager (or at
least an optical part thereof) could be provided in a separate pod
attached to the rest of the vessel.

[0024] The housing is advantageously designed to withstand external
pressures of at least 2 bars; preferably at least 10 bars; and possibly
at least 100 bars. In some embodiments where a vessel in accordance with
the invention is required to be used in the very deepest parts of the
ocean it may be necessary for the housing to withstand pressures of the
order of 1000 bars.

[0025] The invention also extends to a method of generating hyperspectral
images. When viewed from a further aspect, the invention provides a
method of imaging material beneath the surface of a body of water
comprising: [0026] illuminating said material with an artificial light
source from beneath the surface of the water; [0027] receiving from
beneath the surface of the water light reflected from said material into
a hyperspectral imager; and [0028] said imager generating hyperspectral
image data from said material, said image data having at least two
spatial dimensions.

[0029] Preferably the apparatus is as described in accordance with the
first aspect of the invention. Preferably the artificial light source is
provided in the same unit, such as a vessel or underwater platform, as
the imager. It is envisaged however that it could be provided on an
attached unit, or even a separate, unconnected unit.

[0030] In a set of embodiments the method comprises the further step of
adjusting the output spectrum of the artificial light source. In some
embodiments the hyperspectral imager is used to determine whether a
desired spectrum for the artificial light is achieved. The method may
comprise the further step of locating a spectral filter in the path of
the artificial light; it may also or instead comprise the step of
selectively illuminating elements from among a set of spectrally-distinct
light-emitting elements.

[0031] In a set of preferred embodiments the apparatus is used to locate
or map the extent of one or more organisms or other material by the
characteristic spectral fingerprint(s) thereof. However this relies on
these spectral fingerprints being known. The spectral fingerprints might
be obtainable from an existing library, database or other source. However
in a preferred set of embodiments a library is built up or extended by
using a hyperspectral imager to obtain a spectral profile of a specimen
(object of interest). That specimen can be identified by other
means--e.g. visually by an expert or by independent analysis--and the
profile associated with the identity of the material. In some preferred
embodiments, a combination of analysis methods are used to build up the
database; especially preferred is to use a hyperspectral imager in
combination with high-precision liquid chromatography (HPLC) and/or
liquid-chromatography mass spectrometry (LC-MS). These latter techniques
are preferably used to isolate and characterise a substance (e.g.
molecules) that contributes to an optical signature for a specimen. For
example, HPLC may be used to characterise optically different types of
chlorophylls and/or carotenoids.

[0032] This is considered to be novel and inventive in its own right and
thus when viewed from a further aspect, the invention also provides a
method of identifying an underwater material comprising: [0033]
analysing a specimen of a material extracted from a body of water using a
hyperspectral imager to determine a hyperspectral profile of said
material and storing said hyperspectral profile; [0034] taking an image
of an underwater scene in a body of water using said hyperspectral imager
or a further hyperspectral imager; [0035] generating an observed
hyperspectral profile from said scene; and [0036] comparing said observed
hyperspectral profile with said stored hyperspectral profile to identify
said material and recording a positive identification if the comparison
is sufficiently close.

[0037] Thus it will be seen by the person skilled in the art that
underwater material can be identified based on a prior analysis of a
sample of that material. The specimen may, for example, be a mineral; a
protein; a pigment; oil; a metal (e.g. copper, iron); disintegrating
metal (e.g. rust); a bacterium; a eukaryote; a marine invertebrate; a
marine vertebrate; microphytobenthos; macrobenthos; a benthic filter
feeder; a phytoplankton; a zooplankton; a larva; a fish; kelp; an alga;
sediment; a biological mat (bacteria and microscopic eukaryotes covering
sediments); a hydrocarbon; vegetation; wood; an artefact (e.g. a
ship-wreck or a lost item); a hydrothermal vent; a cold seep; or a
plurality, or any combination, of the above.

[0038] Imaging may be conducted near the water surface, within the water
column or on the bottom, both for marine and fresh water.

[0039] Once reflectance, R(lamda), and/or transmission, T(lamda) (where
lamda is the wavelength of light) characteristics are obtained for an
object of interest, preferably embedded in water to mimic natural
conditions, this information can further be used to calibrate and
compensate for the effects of optical path length in water masses of
different types (e.g. case I and II waters where the content of
phytoplankton, coloured dissolved organic matter and suspended matter
needs top be adjusted for since they will alter the spectral
characteristics of the emitted light to the hyperspectral imager due to
different spectral attenuation coefficients, K(lambda), in the water).

[0040] Measurements of R(lamda) from a given object of interest made under
controlled conditions may be used to adjust for the optical path length
(distance from the light source to the object and back to the
hyperspectral imager) and/or to determine optical characteristics of the
intervening water.

[0041] Preferably the apparatus comprises an optical sensor and means for
estimating a spectral attenuation coefficient of the ambient water using
an output from said optical sensor. Preferably such estimations are made
continually or continuously. Preferably these estimations are used to
adjust the output of the artificial light source; e.g. to tune the
spectral output of one or more lamps (LED, halogen, HID, etc.) so that a
predetermined light spectrum will be received at a target object and/or
to compensate for the attenuation of reflected or emitted light returning
to the apparatus. The predetermined light spectrum may be a substantially
uniform energy across the visible spectrum e.g. 400-700 nm (i.e. white
light), or it may be of any other appropriate shape.

[0042] Preferably the method comprises the step of storing said
hyperspectral profile in a database of hyperspectral profiles. Preferably
the method then also comprises the step of retrieving the hyperspectral
profile from the database. This allows, for example, entirely new
chemical species and/or biological entities, previously unknown to man,
to be highlighted as they will not be found to be in the database of
known substances. Such discoveries may have applications to the food,
energy and pharmaceutical industries (e.g. bio-prospecting), among
others.

[0043] Preferably the same hyperspectral imager, or one with the same
optical characteristics is used. In this way, no correction for optical
artefacts unique to a particular imager is required.

[0044] Preferably the step of taking an image of an underwater scene
comprises use of apparatus according to the first aspect of the
invention.

[0045] Data are preferably stored on a hard disk. Analysis of the data may
be performed; e.g. discriminant analysis, principal component analysis,
standard error of replicate measurements, or mean coefficient of
variation. The step of recording a positive identification could comprise
displaying on a display or storing in a volatile or non-volatile memory
or other digital data storage medium.

[0046] Preferably the step of analysing comprises using the hyperspectral
imager in an apparatus comprising an objective lens, e.g. by coupling the
hyperspectral imager to a microscope. Preferably the specimen is
submerged in liquid, preferably water, preferably seawater. Many
materials and objects, including aquatic specimens such as algae, have
different spectral characteristics when they are in water compared with
in air. There are therefore significant advantages in analysing them in a
liquid.

[0047] It will be appreciated that, in addition to having advantageous
optical effects (e.g. no reflected light from light source, imitating the
spectral characteristics of the object of interest in situ under
controlled conditions in the laboratory), the apparatus of this aspect of
the invention allows controlled measurements in the laboratory of marine
organisms of different taxa to be taken in vivo (i.e. with the specimen
alive and in good shape). Nonetheless, it may be desirable on occasions
to generate hyperspectral images of specimens that are dead or decaying.

[0048] The apparatus may further comprise additional means for determining
in vivo spectral absorption or fluorescence excitation spectra; or for
performing high precision liquid chromatography (HPLC), liquid
chromatography mass spectrometry (LC-MS), or nuclear magnetic resonance
spectroscopy (NMR). These additional means may facilitate the isolation,
identification, characterisation and quantification of entities such as
pigments or other bio-molecules or bio-active molecules; this information
may subsequently be used for in situ underwater bio-prospecting of
substances of interests (e.g. bioactive substances). It may thereby be
possible in situ to identify an object of interest and also to determine
its optically-active chemical composition.

[0049] For example, a mat of cyanobacteria on a seafloor may give an
hyperspectral image reflectance drop at 440, 490, 545 and 680 nm. From
previous HPLC analysis it is known that the 440 and 680 nm peaks are
related to the absorption peaks of Ch1 a; the 490 nm peak corresponds to
zeaxanthin; and the 545 nm peak corresponds to phycoerythrin. If some of
the pigments were unknown, subsequent analysis could be performed using
LC-MS to find the molecular weight of the given compound; this would
allow it to be characterised and added to the database.

[0050] This is considered to be novel and inventive in its own right and
thus when viewed from a further aspect, the invention also provides a
method of identifying an underwater material comprising: [0051] taking
an image of an underwater scene in a body of water using a hyperspectral
imager; [0052] generating an observed hyperspectral profile from said
scene; and [0053] using a database to compare said observed hyperspectral
profile with a stored optical profile to identify a molecule and
recording a positive identification of that molecule in the scene if the
comparison is sufficiently close.

[0054] The molecule may be a pigment such as a chlorophyll, carotenoid,
phycobiliprotein or axylene. Preferably a plurality of different
molecules are identified in the scene and preferably the method further
comprises the step of identifying said material from said identification
of the molecule(s).

[0055] In any of the foregoing aspects, the hyperspectral imaging
component is preferably arranged to distinguish between wavelengths to a
resolution finer than 10 nm; more preferably between 0.5 and 2 nm; and
most preferably finer than 1 nm; e.g. 0.5 run. Advantageously, the
spectral resolution of the imaging component is adjustable; preferably
while the apparatus is deployed. Thus the spectral resolution can be set
to match the prevailing conditions, noting that the signal-to-noise ratio
may be improved if the spectral resolution is made coarser. For example
in murky waters or when imaging far-away objects, the spectral resolution
may be made coarser to, say, between 5 and 10 nm, so as to enhance the
signal-to-noise ratio (at the expense of spectral resolution). The
hyperspectral imaging component is preferably arranged to image over the
whole spectrum of visible light; e.g. 400-700 nm. It may alternatively or
additionally be arranged to image outside the visible spectrum; e.g. at
wavelengths below 400 nm and/or above 700 nm.

[0056] The hyperspectral imaging component preferably has a maximum
dimension less than 1 metre and more preferably less than 50 cm; e.g.
between 20 and 30 cm.

[0057] Preferably it has a second-largest dimension less than 50 cm; more
preferably less than 10 cm; e.g. approximately 5 cm. The person skilled
in the art will appreciate that this is considerably smaller than many
previous hyperspectral imagers; this allows the present imaging component
to fit into commercially-available UUVs, AUVs, underwater gliders and
ROVs.

[0058] The hyperspectral imaging component of the present invention is
preferably also under 5 kg in weight; more preferably under 1 kg; e.g.
between 500 and 1000 g. It preferably has a power consumption of less
than 10 W; more preferably less than 5 W; most preferably less than 2 W.

[0059] When viewed from another aspect the invention provides an apparatus
for imaging a specimen comprising an objective lens, a hyperspectral
imager in optical communication with said lens, a vessel suitable for
holding a specimen in liquid such that at least a part of said specimen
is situated in the focal plane of said lens.

[0060] The invention extends to a method of imaging a specimen immersed in
liquid in a container using a hyperspectral imager.

[0061] Thus it will be seen that an apparatus is provided which may be
used in a laboratory situation to analyse samples in a fluid using a
hyperspectral imager. As above preferably the liquid is water such as
seawater.

[0062] The specimen could be static during the analysis. Preferably
however the apparatus comprises means operable to move said vessel
relative to said lens in a direction parallel to said focal plane. This
allows a hyperspectral image with two spatial dimensions to be built up.
This might be useful for example in establishing an area of an object
comprising a certain material and obtaining an averaged hyperspectral
profile across that area. Thus a preferred method comprises moving the
specimen relative to an objective lens of said imager in a direction
parallel to the focal plane of the lens and forming a two-dimensional
image of the specimen.

[0063] Preferably the apparatus comprises an artificial light source e.g.
a halogen, xenon, metal halide (HID, light arc) lamp. The advantages of
an artificial light source are discussed above in relation to the first
aspect of the invention. Light from the light source may be directed onto
or through the specimen by optical diffusers, optical fibres and/or
mirrors. The apparatus may be arranged to generate images using light
reflected from the specimen, or light transmitted through the specimen,
or both.

[0064] There may be an air gap between the front of the objective lens and
the surface of the fluid, but preferably the objective lens is at least
partially immersed in the fluid. Thus optical interference due to the
light passing through air between the fluid surface and the objective
lens is avoided.

[0065] Preferably this method uses apparatus as set out in the preceding
aspect of the invention.

[0066] Various aspects and features of the invention have been set out
above. Features described with reference to one aspect should not be
understood as being limited to that aspect only, but rather as also being
applicable to any of the other aspects where appropriate.

[0067] Certain preferred embodiments of the invention will now be
described, by way of example only, with reference to the accompanying
drawings, in which:

[0068]FIG. 1 is a schematic, perspective drawing of the principle
components of a hyperspectral imager as used in embodiments of the
invention;

[0069]FIG. 2 is figurative diagram showing a vertical cross-section
through an underwater vehicle embodying the invention;

[0070]FIG. 3 is a perspective drawing of the exterior of an underwater
hyperspectral imager embodying the invention;

[0071]FIG. 4 is a perspective drawing of a light source for use with
embodiments of the invention;

[0072]FIG. 5 is a perspective view of a hyperspectral microscopic imager
in accordance with the invention; and

[0073] FIG. 6 shows the analysis of a specimen of a red alga using a
magnifying hyperspectral imager in accordance with the invention.

[0074] First an example of the use of a hyperspectral imager to form an
image having two spatial dimensions will be described with reference to
FIG. 1. FIG. 1 shows how light passes from a scene 2 through the optics
of a push-broom hyperspectral imager during the capture of a single
frame. Only a thin strip 4 of the scene is imaged during each time frame,
extending in the direction of the Y axis and having width ΔX. Light
from the scene first passes through an objective lens 8 which focuses it
through an entrance slit 10. The slit excludes light other than that
emanating from the strip 4. Its width is set to relate desired width
ΔX to the width of a single row of pixels of a CCD image sensor 18.
A collector lens 12 then directs light through a grism 14, which is a
combination of a grating and a prism arranged to create a dispersed
spectrum. The spectral dispersion occurs over the X axis, orthogonal to
the spatial dimension Y of the strip 4. A camera lens 16 then focuses the
spectrally dispersed light onto a CCD image sensor 18.

[0075] In order to build up an image of a two-dimensional scene, the
objective lens 8 and other optics are, over time, moved laterally
relative to the scene 2 in the direction of the X axis. The speed of
motion is determined such that each sequential frame captures a strip 4
of the scene along the Y axis immediately adjacent the preceding strip.
The sequential frames can be processed and composed to generate a
hypercube. If desired, this hypercube can be used to generate
two-dimensional flat greyscale images indicating light intensity at each
pixel for a given single optical wavelength range. The wavelength
resolution of the apparatus is determined by the number of pixels on the
CCD sensor 18 in the direction of the X axis.

[0076]FIG. 2 shows an autonomous underwater vehicle (AUV) 20 according to
an embodiment of the invention in a body of water 22 above a seabed 24. A
suitable AUV is the REMUS developed by the Woods Hole Oceanographic
Institution. The AUV 20 comprises a tail section 26 containing the
propulsion motor and controller circuitry for a propeller 28. A mid-body
section 30 houses various operational components of the vehicle. Between
the mid-body section 30 and a nose cone 32 is an optics section 34. The
optics section 34 comprises a watertight chamber carrying a hyperspectral
imager and a light source (not shown). A transparent outlet window 36
allows light 40 from the light source to emerge towards a scene of
interest, such as the seabed 24. Light 42 returning from the scene enters
through a transparent inlet window 38 behind which is located the
objective lens 8 of a hyperspectral imager.

[0077]FIG. 3 shows another embodiment of an underwater apparatus 44
embodying the invention. This apparatus 44 is not self-propelling but
rather can be lowered into the water attached to a floater and so be
immersed in the water for towing by a boat for example, or carried by a
human diver. It comprises a watertight housing 46 made of aluminium or
marine steel having a transparent window 48 made of soda glass or quartz
to allow the passage of light into, and optionally out of, the imager 44.
It also has a display panel 50 for turning the system on and off, tuning
the frame, gain, iris and gamma controls. Inside the housing 46, there is
a hyperspectral imager, batteries and video recorder and there may be one
or more lamps. The apparatus 44 may also carry external underwater lamps
(not shown) such as an Underwater Kinetics Light Cannon 100, which can be
used to obtain 6000 degrees Kelvin colour temperature. The imager can be
used in any orientation; i.e. it can be pointed horizontally, up or down.

[0078] In both cases above the apparatus could carry several lamps which
can be used individually or in combination to provide a customised
illumination. This can be used to minimise the effects of absorption and
scattering in the water between the light source, imaged material and the
imager, and can also ensure that the correct wavelengths in the imaged
material are excited.

[0079] The lamp 52 shown in FIG. 4 is also suitable for use with imagers
embodying the invention, such as those of FIGS. 2 and 3 and takes the
idea of blending light sources one step further. The lamp 52 comprises a
plurality of light emitting diode (LED) lamps 54 which can be selectively
illuminated. Some of the LEDs are white, emitting light in the range
350-800 nm. Others are blue (emitting light in 400-500 nm range), green
(500-600 nm), and red (600-700 nm).

[0080] The spectrum of light emanating from the lamp 52 can be tuned by
selecting which LEDs to activate, depending on the optical properties of
the water (which vary with distance to the target object due to the
spectral attenuation coefficient of water, and which can vary due to
optically-active components such as phytoplankton, coloured dissolved
organic matter and total suspended matter).

[0081] Either of the two underwater apparatus described above can be used
to capture and record two-dimensional hyperspectral images beneath the
water. By carrying its own artificial light source, the imaging apparatus
can measure much more accurate hyperspectral information than is possible
using airborne remote sensing. For example the effects of solar
horizontal, and of atmospheric scattering and distortion are removed.
Moreover the path length of the emitted and reflected light through the
water can be relatively short, whatever depth the imaged material is at.

[0082] One application of the principles of the invention is in mapping or
prospecting for materials by using a database of spectral profiles that
correspond to known materials such as particular compounds, substances or
organisms to compare against the spectral profiles measured from the
captured images. The spectral profiles on the database might be
commercially or publicly available. However below a method of building up
or adding to such a database will be described.

[0083]FIG. 5 shows a hyperspectral microscopic imager 56 for use in the
method mentioned above forming an embodiment of another part of the
invention. The imager 56 comprises a microscope component 60, adapted
from a conventional optical microscope, such as a Leitz Leca MS5
microscope (1-80x), and a hyperspectral imaging component 58, such as an
Astrovid StellaCam II Video Camera [AV-STCA2] with a pixel array of
640×480, containing optics as described with reference to FIG. 1.
The objective lens of the hyperspectral imaging component 58 may, by way
of example, have a focal length of 25 mm and f:1.6.

[0084] The hyperspectral imaging component 58 has an image capture means;
for example an ARCOS pocket video recorder AV400 capturing AVI video at
25 frames/sec. In one example, each video frame recorded (spectral
profile), consists of the light spectrum from 363 to 685 nm dispersed
over 640 pixels, giving a resolution of 0.5 nm/pixel. The spatial
resolution perpendicular to the moving direction in this example is 193
pixels.

[0085] The imager 56 further comprises a moveable platform 62, which can
be moved in the direction indicated by the arrow by a stepper motor
located underneath the platform. By way of example, the stepper motor may
have a gear exchange of 1:500 giving a speed of 2.59 mm/sec. The platform
62 carries a watertight sample container 64, such as a Petri dish, which
can hold a specimen in a volume of liquid. The container 64 is also
arranged to direct light through a specimen from beneath, for example by
means of a mirror and a diffuser, when determining optical transmission
characteristics of a specimen; or with a light source above for
determining optical reflectance. The imager 56 also comprises one or more
light sources directable onto the upper surface of a specimen, preferably
from an off axis angle such as at 45 degree to the vertical. The same
light source may be used for either transmissive or reflective analysis
and may consist of a halogen or other light source directed appropriately
through two fibre optic bundles. This light source can be used when
determining the reflectance characteristics of a specimen. The objective
lens of the microscope component 60 may be lowered into the fluid carried
in the sample container 64, to mitigate any optical interference that
might be caused due to the fluid-air and air-lens boundaries when the
objective lens is located out of the fluid.

[0086] In use, a sample is placed in fluid; such as sea water, in the
sample container 64. The stepper motor moves the platform 62 in the
direction of the arrow while the hyperspectral imaging component 58
captures sequential spectral image strips across the specimen orthogonal
to the direction of motion. These strips can be combined as explained
above with reference to FIG. 1. In particular, processing may be
performed using YaPlaySpecX software (Fred Sigemes, UNIS, cf. Sigemes et
al. 2000 Applied Optics) to compose monochromatic images from an AVI
video, forming an spectral image cube. Depending on the light source
selected, two- dimensional images of either spectral transmittance or
spectral reflectance of the specimen in the liquid can be generated at
high magnification through use of the imager 56.

[0087] If desired, average spectral characteristics (with statistical
information on e.g. error estimates) for an area of interest captured
with the hyperspectral microscopic imager 56, can be found by averaging
information from an image hypercube in the spectral direction. The
average spectral characteristics measured for reflection, Er(lamda)
(mW/nm), or transmission, Et(lamda) (mW/nm), may be adjusted for the
halogen lamp (or other light source) radiant intensity spectrum for
reflection, Ehr(lamda) (mW/nm), and for transmission,
Eht(lamda) (mW/nm), to give a comparable reflectance or
transmittance spectrum with optical density. The dimensionless
reflectance spectra is then R(λ)=Er(lamda)/Ehr(lamda) and
the dimensionless transmittance spectra is
T(lamda)=Et(lamda)/Eht(lamda).

[0088] FIG. 6 shows an image A of a specimen of a red alga to be analysed
using a magnifying hyperspectral imager in accordance with the invention.
It also shows a magnified monochromatic image B of the specimen in water
(at 600 nm wavelength) captured using the hyperspectral imager. Three
distinct regions 1, 2, 3 are indicated, for which the average
reflectance, R(lamda), over the region is to be determined. FIG. 6-C
shows the R(lamda) spectra 1, 2, 3 obtained. It also shows the
corresponding spectral absorbance spectrum OD, measured with a
spectrophotometer, which validates the reflectance measurements (they
should be inversely related). The reflectance measurements have been
adjusted to compensate for the halogen lamp radiant intensity spectrum,
Eh(λ).

[0089] Once an averaged spectrum for a region of interest has been
obtained, this can be used to identify other instances of the same
material in other situations; in particular, it can be used with the
apparatus described earlier to identify the same material underwater
using in situ hyperspectral imaging apparatus.